feat(ollama): periodically refresh models (#2805)

For self-hosted providers like Ollama (or vLLM), the backing server is
running a set of models. That server should be treated as the source of
truth and the Stack registry should just be a cache for those models. Of
course, in production environments, you may not want this (because you
know what model you are running statically) hence there's a config
boolean to control this behavior.

_This is part of a series of PRs aimed at removing the requirement of
needing to set `INFERENCE_MODEL` env variables for running Llama Stack
server._

## Test Plan

Copy and modify the starter.yaml template / config and enable
`refresh_models: true, refresh_models_interval: 10` for the ollama
provider. Then, run:

```
LLAMA_STACK_LOGGING=all=debug \
  ENABLE_OLLAMA=ollama uv run llama stack run --image-type venv /tmp/starter.yaml
```

See a gargantuan amount of logs, but verify that the provider is
periodically refreshing models. Stop and prune a model from ollama
server, restart the server. Verify that the model goes away when I call
`uv run llama-stack-client models list`

llama_stack/distribution/routing_tables/models.py

@@ -80,3 +80,34 @@ class ModelsRoutingTable(CommonRoutingTableImpl, Models):
         if existing_model is None:
             raise ValueError(f"Model {model_id} not found")
         await self.unregister_object(existing_model)
+
+    async def update_registered_models(
+        self,
+        provider_id: str,
+        models: list[Model],
+    ) -> None:
+        existing_models = await self.get_all_with_type("model")
+
+        # we may have an alias for the model registered by the user (or during initialization
+        # from run.yaml) that we need to keep track of
+        model_ids = {}
+        for model in existing_models:
+            if model.provider_id == provider_id:
+                model_ids[model.provider_resource_id] = model.identifier
+                logger.debug(f"unregistering model {model.identifier}")
+                await self.unregister_object(model)
+
+        for model in models:
+            if model.provider_resource_id in model_ids:
+                model.identifier = model_ids[model.provider_resource_id]
+
+            logger.debug(f"registering model {model.identifier} ({model.provider_resource_id})")
+            await self.register_object(
+                ModelWithOwner(
+                    identifier=model.identifier,
+                    provider_resource_id=model.provider_resource_id,
+                    provider_id=provider_id,
+                    metadata=model.metadata,
+                    model_type=model.model_type,
+                )
+            )